Water holding tanks are commonly utilized to store well water. Recently, a water holding tank that utilizes a blow-molded construction has been introduced. See our copending patent application Ser. No. 10/794,013. Periodically, water must be added to the holding tank in order to refill the tank and/or to aerate the water in the tank so that it is safe for drinking. Most known holding tanks employ an electrically operated solenoid valve that is opened as needed to introduce water to the tank. This type of valve has caused maintenance and repair problems. Governmental codes presently require the electrical solenoid to employ a ground fault. Because the solenoid is installed in proximity to water, it is susceptible to short-circuiting and malfunction. Frequent, inconvenient and expensive service calls are often required.